1. Field of the Invention
The invention relates generally to navigation and more specifically to equipment and methods for finding ones position on a map with the aid of a global positioning system receiver.
2. Description of the Prior Art
Global positioning system (GPS) receivers conventionally output position indications in terms of longitude and latitude. Relating that information to a road map, atlas or topographic map has been difficult for lay people, and errors in understanding one's real position relative to a map are frequently made.
Topographical map users need a quick and easy method to determine and record their precise position on any topographical (TOPO) series map. Such maps have a datum located somewhere on the map, such as at a bottom right corner, e.g., the south east corner, that provides the latitude and longitude at that point. The map further provides a scale factor that can be used to convert, for example, inches on the map to miles over the terrain. Users could benefit from a system that could provide position information in any one of several different formats, starting from four inputs consisting of a datum input, a scale factor, and the horizontal and vertical distances on the map from the datum. A GPS receiver that provided current position information from a user selected reference point, such as the south-east datum of a map page, would be useful if inches "over and up" from the datum were displayed on the GPS receiver's screen.
Besides the longitude-latitude format, other formats for position identification include universal transverse mercader (UTM), Maidenhead, TRIMBLE GRID LOCATOR.TM., OSGB and Thomas Brothers.TM. Maps. Maidenhead is a system used by the world's amateur radio operators to describe locations in alternating sequences of two letters followed by two digit numbers. Each pair adds precision to the position description, and Maidenhead coordinates can be readily communicated over radio channels, even when the reception is poor. TRIMBLE GRID LOCATOR (TGL) is a proprietary map coordinate system marketed by Trimble Navigation (Sunnyvale, Calif.) for use with GPS receivers. The TRIMBLE ATLAS is based upon the North American Datum, 1927 (AND 27).
A regional map of the United States is provided in atlas form for the TGL system and provides a regional map scale of one inch to thirty miles and an area map scale of one inch to five miles. Table I lists the nine regions of the United States.
TABLE I ______________________________________ Region 1: Pacific Northwest Region 2: Mountain Region 3: North Central Region 4: Great Lakes Region 5: Northeast Region 6: Pacific Southwest Region 7: Four Corners Region 8: South Central Region 9: Southeast ______________________________________
Area pages following each regional section provide close-up views of selected metropolitan areas, and show an entire street network. For example, San Jose, Calif., is shown on a page identified "R6 263" for region six, area page 263. On that page in the atlas, grid coordinates are provided A-L left to right, and 1-11 top to bottom. The San Jose International Airport (SJC) can be seen as being located in grid J5, area page 263, R6. This could alternatively be expressed as "R6,263,J5".
Each page and grid location can be sub-divided into nine equal sub-grids, such as in Table II. This allows for greater resolution in pinpointing a given location. In the example, SJC is located in sub-grid "UR", making it, "R6,263,J5,UR".
TABLE II ______________________________________ UL UC UR ML MC MR LL LC LR ______________________________________
The abbreviations used for the nine equal sub-grids are expanded in Table III.
TABLE III ______________________________________ UL Upper Left UC Upper Center UR Upper Right ML Middle Left MC Middle Center MR Middle Right LL Lower Left LC Lower Center LR Lower Right ______________________________________
Given the prior art, it would be difficult to find one's position using such an atlas, given only longitude-latitude information, such as is provided by a conventional GPS receiver. A GPS receiver that would display TGL information directly for a user's position would be more useful.
GPS receivers conventionally provide for input of a series of waypoints on a path to a goal destination. Off-track information is typically provided real time to inform a user how far off, left or right, the actual track is off from the ideal track. Such information is not very useful to hikers who are more concerned with what their heading should be, with regard to where they are presently. A target tracking display on a GPS receiver is needed to show users their current position, relative to their goal destination. A distance and speed indication would also be useful.